Question

Astronomers have discovered a planetary system orbiting
thestar Upsilon Andromedae, which is at a distance 4.2 1017
mfrom the earth. One planet is believed to be located at a
distanceof 1.7 1011
m from the star. Using visible lightwith a vacuum wavelength of 550
nm, what is the minimum necessaryaperture diameter that a telescope
must have so that it can resolvethe planet and the star?
m